1. Field of the Invention
The present invention relates generally to an AAL2 (ATM Adaptation Layer 2) switching apparatus and method, and in particular, to a switching apparatus and method using a memory mapping technique.
2. Description of the Related Art
In general, ATM (Asynchronous Transfer Mode) refers to an ATDM (Asynchronous Time Division Multiplexing) packet transmission technique. In the ATM, a basic information transmission unit becomes a “cell.” In the ATM, every type of information is handled in an ATM cell with a fixed length of 53 bytes. Further, in the ATM, a protocol is simplified on the assumption that information is transmitted at high quality. Consequently, a switching process can be realized by hardware, and a switching delay can be reduced, thus achieving high-efficiency packet switching. Meanwhile, AAL serves to provide services having different communication characteristics in an ATM layer, such as voice, image and data services, to an upper application in a proper format. In particular, AAL2 is a protocol for providing a timing-dependent service such as voice and image services encoded at a variable rate in a transceiver.
of 53 bytes of the ATM cell, 5 bytes are used for a header and the remaining 48 bytes are used for an information field. The ATM cell, a data stream with a fixed length, becomes a unit of multiplexing and switching. The header includes VCI (Virtual Channel Identifier), VBI (Virtual Bus Identifier) and VPI (Virtual Path Identifier), for identifying a connection to which the cell belongs, and further includes CLP (Cell Loss Priority) for indicating whether to discard the cell during traffic congestion, PT (Payload Type) for distinguishing network control information, and HEC (Header Error Control) for detecting and controlling a header error.
However, since the ATM cell has a fixed of 53 bytes, a band (or byte) waste problem may occur when small-sized information such as voice information is transmitted. For example, since the 53-byte ATM cell is used even when transmitting 2 or 3-bytes of small information, 45 or 46 bytes of the 48-byte information field are wasted. To solve this problem, a CPS (Common Part Sublayer) packet has been proposed. The CPS corresponds to the AAL2, and the CPS packet has a variable length depending upon the size of information to be transmitted. During information transmission using the CPS packet, a plurality of CPS packets may be included in the information field of the ATM cell. In order to transmit information using the CPS packets, a new switching apparatus and method is required. Conventionally, a switching apparatus for switching packets in the AAL2 layer is realized by software. However, when the switching apparatus is realized by software, the capacity can hardly exceed 4K CIDs (Channel Identifiers) due to its performance limitations. However, when the AAL2 switching apparatus is realized by hardware, a large number of flip-flops (twice the number of connections supported) are required in order to convert a specific input CID into a specific output CID. Further, an FPGA (Field Programmable Gate Array) capacity for realizing the switching apparatus is increased.